NEW YORK (Reuters Health) - Devices that help lung disease patients have oxygen therapy on-the-go may not always perform consistently -- and may in some cases provide users with inadequate oxygen when they are active, a new study suggests.

The concern, say researchers, is that patients and doctors may interpret any resulting activity limitations as a sign that the lung disease is worsening, when it could instead be a shortcoming of the oxygen device.

The devices in question, known as oxygen conservers, are used mainly by people with chronic obstructive pulmonary disease (COPD), a group of lung diseases that includes emphysema and chronic bronchitis.

Oxygen conservers attach to the portable oxygen cylinders that many COPD patients carry because they need supplemental oxygen as they walk, climb stairs or perform other daily activities. The conservers are designed to dole out a set oxygen dose each time a person inhales; this allows the cylinders' oxygen supply to last longer than it would if the oxygen flow were continuous.

In the new study, researchers at Case Western Reserve University in Cleveland, Ohio, tested four of what they describe as the most widely used oxygen conservers on the market. (They would not identify the specific brands.)

The researchers first bench tested each conserver to gauge performance, then had 13 COPD patients use each device in random order, at rest and during treadmill walking tests carried out over several weeks.

For comparison, the patients were also evaluated while breathing standard room air and while a wall unit supplied the room with 2 liters of oxygen per minute -- the dose each patient required.

Overall, the study found, the conservers' performance varied from product to product. And none of the devices consistently performed up to technical expectations, according to findings published in the American Journal of Respiratory and Critical Care Medicine.

One conserver was no better than breathing standard room air when it came to maintaining patients' blood oxygen levels during rest or exercise, senior researcher Dr. Edward Regis McFadden, Jr. told Reuters Health.

Last Updated: 2010-02-26 12:46:17 -0400 (Reuters Health)

The other three conservers performed better, he said, but patients' oxygen levels dipped when they walked on a treadmill compared with their levels at rest. In contrast, patients' oxygen levels were maintained when the room was supplied with oxygen.

As a group, the conservers' actual oxygen doses differed from what was expected based on bench testing. Two devices consistently delivered less than the expected amount of oxygen during rest and exercise, according to the researchers.

Moreover, they found, the amount of walking each study participant accomplished varied according to which conserver he or she was using.

The problem, according to McFadden, is in the technical aspects of the conservers.

The devices, he said, are unable to keep up with a person's breathing, matching each breath with a consistent dose of oxygen. All of the devices in this study showed "suboptimal activation with breathing," the researchers write.

The findings highlight an "extremely important" issue for patients and doctors to be aware of, said Dr. Barry Make, co-director of the COPD program at National Jewish Health in Denver. Make was not involved in the current study.

At National Jewish, a leading hospital for respiratory diseases, patients prescribed an oxygen conserver undergo testing to make sure the device provides enough oxygen at rest and during activity, Make said in an interview. A sensor placed on the finger gauges the concentration of oxygen in the blood.

The current findings emphasize the importance of such testing, according to Make. He also pointed out that patients' oxygen needs change over time, and that he and his colleagues routinely reassess how well patients' oxygen conservers are working -- at least yearly.

Make and McFadden both said that COPD patients with any concerns about their oxygen conservers' performance should talk with their doctors.

But McFadden and his colleagues also argue that their findings highlight a need for "uniform performance standards" for oxygen conservers -- set, McFadden said, by government regulators, based on advice from professional medical organizations.

As it stands, oxygen conservers do not have to go through clinical testing -- that is, studied in actual patients -- before going on the market.

All conservers, McFadden noted, are considered to be "variations on a basic theme." So they fall under a Food and Drug Administration process that gives clearance to devices based on bench testing and a comparison to existing products.

"That is based on the idea that they are all the same, and they will work the same," McFadden said. But the current findings, he said, indicate that "engineering equivalency" does not mean equivalent performance when people use the conservers.

One company that makes the conservers, Elyria, Ohio-based Invacare Corp, said that there are roughly 40 conserver models on the market, and the performance of four cannot be generalized to the entire market.

"There is a large, and growing, body of peer-reviewed studies that demonstrate that conserving devices are able to meet the clinical needs of patients at rest, during exercise and even while sleeping," Joseph Lewarski, vice-president of Invacare's Respiratory Group, said in a written response to questions from Reuters Health.

Heather Anusbigian, marketing administrator for Inovo/CHAD Therapeutics, which makes another device, said that "the findings point out the need for further studies pertaining to the efficacy of oxygen conserving devices."

In their own studies, Inovo/CHAD "reached different conclusions than those found in the Case Western Reserve study," she told Reuters Health by email. "Most oxygen conserving device users are able to achieve adequate oxygen saturation levels either during rest or activity." Field testing, she said, "clearly indicates that these devices are working."

Asked about the idea of setting "uniform performance standards" for the devices, Invacare's Lewarski said that "we do and would continue to comply with all regulatory requirements applied to the technologies we develop."

However, Lewarski added, "the challenge associated with standardizing all technical specifications related to oxygen conservers is objectively and scientifically determining what standards are ideal for all devices and patients."

Invacare provided some of the funding for the study.

SOURCE: American Journal of Respiratory and Critical Care Medicine, online February 4, 2010.